April 30, 2013

Singing Humpback Whales Tracked In Northwest Atlantic Feeding Grounds

Humpback whales are known for their songs that can be heard from miles away and new research from a team of American biologists has detailed the whales singing habits as they roam the feeding grounds of the northwest Atlantic.

The study´s findings, which were published in the open access journal PLOS ONE, emphasize the usefulness of passive acoustics listening techniques in monitoring animal activity.

“We have monitored and acoustically recorded whale sounds for years, and are now able to ℠mine´ these data using new computer software applications and methods," said co-author Sofie Van Parijs, who heads the passive acoustics group for the National Oceanic and Atmospheric Administration´s Northeast Fisheries Science Center (NEFSC).

“Passive acoustic tracking has enabled us to localize humpback whale song to study the movements of individual whales, and to relate the singing to specific behaviors,” Van Parijs explained. “This has never before been accomplished for singing humpbacks on a northwest Atlantic feeding ground.”

Starting in 2007, NEFSC researchers have used continuous passive acoustic monitoring to study ocean sounds in the Stellwagen Bank National Marine Sanctuary, a feeding ground for whales in the southern Gulf of Maine. A collection of 10 bottom-mounted marine autonomous recording units (MARUs) were deployed in the sanctuary for four straight three-month periods during 2009. The MARUs were spaced three to six miles apart and shifted seasonally to areas with the highest whale concentrations.

The researchers also attached several multi-sensor tags to whales. These tags enabled the team to monitor whale location and swimming velocity.

The research team collected 43 song sessions, each lasting from 30 minutes to eight hours. Most of the whales were actively swimming as they sang; from slow, aimless meandering to a faster directional swim.

Even though humpbacks were in the area, the researchers didn´t record any songs during summer and winter. Humpback whale singing was typically heard from April through May, following the spring migration from tropical waters. A higher frequency of songs was also heard from August to December before the annual fall migration.

“Passive acoustic tracking of humpback whales and other cetacean species provides an opportunity to collect data on movement patterns that are difficult“or impossible“to obtain using other techniques,” noted lead author Joy Stanistreet, a researcher at NEFSC´s Woods Hole Laboratory at the time of the study.

In their conclusion, the marine researchers said that passive acoustic localization and tracking methods could be combined to better understand the distribution, abundance, and densities of humpbacks and other whale species. They said that the results of these tracking techniques could inform and enhance marine mammal conservation and management efforts, especially for threatened or endangered species.

Currently, the worldwide humpback whale population is estimated to be over 80,000. The past 20 years has seen a steady improvement in the humpback´s conservation status as the species was considered “vulnerable” in 1996 and was hunted to near extinction throughout much of the 20th century. Today, the whales´ biggest threat comes from collisions with ships and noise pollution from underwater human activities.